Research On Pretreatment And Open Fermentation Of Sophora Flavescens Residues For L-lactic Acid Production

With the increasing application of Chinese herbal medicine and Chinese patent medicine,a large amount of Chinese herb residues are inevitably produced annually.Resourcization of these herb residues can significantly improve the economic benefit for pharmaceutical plants and also protect the environment.In the current study,L-lactic acid was produced from open fermentation of Sophora flavescens residues(SFR).The operation parameters for pretreatment and fermentation of SFR were optimized,and the bacteria community changes and product formation kinetics during fermentation were also analyzed.By comparing the enzymatic hydrolysis performance of thermal,H2SO4,and NaOH pretreated SFR,and NaOH pretreatment was found to be the most suitable pretreatment method for SFR.This is because that NaOH pretreatment can remove most of the lignin and cause deacetylation of the hemicellulose in the substrate,which made the surface of the substrate become rough and loose,thus increasing the accessibility of cellulase and enhanced the enzymatic hydrolysis efficiency of cellulose.The optimum operation conditions for pretreatment were:NaOH concentration 1.0%(w/v),solid-liquid ratio 1:10,temperature 80?,and processing time 60 min.Under this condition,the reducing sugar yield of NaOH pretreated SFR reached 85.0%.The Oxford-cup experiments found that the medicinal components(Sophora Flavescens alkaloids)remained in the SFR was not high enough to affect the growth and fermentation of Lactobacillus casei.The optimum operation conditions of L-lactic acid production during the open fermentation of SFR were through simultaneous saccharification and fermentation,and intermittently adjusting the pH to 8.5 with sodium hydroxide solution at a time interval of 12 h.After 60 h fermentation,the concentration,yield and productivity of lactic acid reached 51.1 g/L,0.85 g/g and 0.85 g/(L h),respectively.The analysis of the bacteria community during the open fermentation found that Lactobacillus casei,the inoculum bacteria,was the absolute dominant bacteria during the lactic acid accumulation stage,with abundance over 99.6%.When the lactic acid concentration reached the highest,the abundance of contaminating microorganisms Bacillus and Clostridium increased,resulting in increased acetic acid concentration.Intermittently adjusting the pH to 8.5 can effectively inhibit the growth and metabolism of ethanol-producing yeast,thus inhibiting the production of ethanol.The reutilization of the pretreated liquor(PL)produced during NaOH pretreatment can significantly improve the lactic acid production.When the PL content in the fermentation medium was 50%,the concentration of lactic acid produced reached 55.1 g/L,which was 34.3%higher than that when no PL was reutilized,and the water consumption decreased by 67.6%.This is possibly because that the addition of PL made the pH more stable,and thus improved the stability of cellulase activity.Moreover,50%PL content could inhibit the growth of the ethanol-producing yeast but had no significant effect on the lactic acid bacteria,and therefore reduced the production of ethanol and increased the lactic acid concentration and yield.The lactic acid production kinetics during the open simultaneous saccharification and fermentation of SFR fitted the reparameterized Logistic model and the Gompertz model.The current study not only provided a cheap raw material for lactic acid production but also realized the resourcization of Chinese herb residues.Therefore,it has important practical significance and application prospect.